This invention relates to a method for the preparation of a polymer of dicyclopentadiene (hereinafter referred to as DCPD). In particular, it relates to employing a metathesis-catalyst system to form a high modulus, high impact strength thermoset poly(DCPD) homopolymer. In a preferred embodiment the homopolymer is formed when two solutions, one a catalyst/monomer mixture and the other an activator/monomer mixture, are combined in a reaction injection molding (hereinafter referred to as RIM) machine and then injected into a mold.
Any good thermoset polymer should meet at least two criteria. It should have desirable physical properties and it should lend itself to easy synthesis and forming. Among the most desirable physical properties for many polymers is a combination of high impact strength and high modulus. A standard test for impact strength is the notched Izod impact test, ASTM No. D-256. For an unreinforced thermoset polymer to have good impact strength, its notched Izod impact should be at least 1.5 ft. lb/in. notch. It is desirable that this good impact strength be combined with a modulus of at least about 150,000 psi at ambient temperature. Thermoset polymers with high impact strength and high modulus find useful applications as engineering plastics in such articles of manufacture as automobiles, appliances and sports equipment. Among the critical factors in the synthesis and forming of a thermoset polymer are the conditions required to make the polymer set up or gel. Many thermoset polymers require considerable time, elevated temperature and pressure, or additional steps after the reactants are mixed before the setting is complete.
While some references of poly(DCPD) have been made in the literature, a thermoset homopolymer having high impact strength and high modulus has never been described. Characteristics of thermoset polymers include insolubility in common solvents such as gasoline, naphtha, chlorinated hydrocarbons, and aromatics as well as resistance to flow at elevated temperatures.
Work has been done on the metathesis copolymerization of DCPD with one or more other monomers to produce soluble copolymers. This copolymer formation has resulted in the production of unwanted insoluble by-products. U.S. Pat. No. 4,002,815, for instance, teaches the copolymerization of cyclopentene with DCPD, describes an insoluble by-product and suggests that the by-product could be a gel of a DCPD homopolymer.
Some work, usually in an attempt to produce soluble poly(DCPD's), has been done on the metathesis homopolymerization of DCPD. Japanese unexamined published patent applications KOKAI 53-92000 and 53-111399 disclose soluble poly(DCPD's). Several syntheses of soluble poly(DCPD) have produced insoluble by-products. Takata et al, J. Chem. Soc. Japan Ind. Chem. Sect., 69, 711 (1966), discloses the production of an insoluble poly(DCPD) by-product from the Ziegler-Natta catalyzed polymerization of DCPD; Oshika et al, Bulletin of the Chemical Society of Japan, discloses the production of an insoluble polymer when DCPD is polymerized with WCl.sub.6, AlEt.sub.3 /TiCl.sub.4 or AlEt.sub.3 /MoCl.sub.5 ; and Dall Asta et al, Die Makromolecular Chemie 130, 153 (1969), discloses an insoluble by-product produced when a WCl.sub.6 /AlEt.sub.2 Cl catalyst system is used to form poly(DCPD).
In U.S. Pat. No. 3,627,739 ('739), a thermoset poly(DCPD) is the object of synthesis. The poly(DCPD) of '739 is brittle, having an Izod impact strength of only 0.78.
Not only is it desirable that the thermoset polymer have high impact strength, but it is also desirable that it be easily synthesized and formed. A RIM process achieves this second goal by in-mold polymerization. The process involves the mixing of two or more low viscosity reactive streams. The combined streams are then injected into a mold where they quickly set up into a solid infusible mass. RIM is especially suited for molding large intricate objects rapidly and in low cost equipment. Because the process requires only low pressures, the molds are inexpensive and easily changed. Furthermore, since the initial materials have low viscosity, massive extruders and molds are not necessary and energy requirements are minimal compared to the injection molding or compression molding commonly used. For a RIM system to be of use with a particular polymer, certain requirements must be met:
(1) The individual streams must be stable and must have a reasonable shelf-life under ambient conditions.
(2) It must be possible to mix the streams thoroughly without their setting up in the mixing head.
(3) When injected into the mold, the materials must set up to a solid system rapidly.
(4) Any additives-fillers, stabilizers, pigments, etc. must be added before the material sets up. Therefore, the additives selected must not interfere with the polymerization reaction.
It can be seen that when developing a RIM process a tradeoff must be made. It is desirable that the polymer set up quickly, but the polymerization cannot be too quick. The components cannot be so reactive that they set up in the mixing head before they can be injected into the mold. Once in the mold, however, the polymer should set up as quickly as possible. It is not desirable that the polymer take a long time or require additional steps to gel completely.
It is known in the prior art to base a RIM system on the combination of two reactive monomers, e.g., the polyol and the diisocyanate monomers employed in a polyurethane system. It is known, but not in the context of a RIM system, to combine two or more reactive parts of a catalyst, where one or both are in solution with the monomer, to form a homopolymer. A process which employs two separate streams based on a two part catalyst system to produce a thermoset polymer in such a manner that the streams can be combined in one place and then rapidly set up in another is unique and is a substantial contribution to the art.
U.S. Pat. No. 2,846,426, Larson, claims the combination of two vapor streams, one containing a vaporizable alkylaluminum compound and the other containing a vaporizable compound of Group IV-B, V-B, or VI-B metal, where at least one of the streams contains a gaseous monomer. The vapor streams are combined and a thermoplastic polymer is formed in the same reaction zone. U.S. Pat. No. 3,492,245, Calderon et al, discloses the in-situ formation of a catalyst system containing an organoaluminum compound, a tungsten hexahalide and a hydroxy compound. Again, the reactive components are mixed and the polymerization of an unsaturated alicyclic compound occurs in the same vessel. U.S. Pat. No. 3,931,357, Meyer, teaches a process for forming a soluble graft copolymer of a polydiene or a polyalkenamer and an unsaturated polyolefin rubber which entails combining a stream containing a metathesis catalyst component from a metal of subgroups V through VII of the periodic table with a stream containing an alkyl or a hydride of a metal from main groups I through VII of the periodic table prior to the metathesis reaction proper. Since the copolymer is soluble, there is no requirement that it rapidly set up.